The present invention relates to a catalyst composition suitably used in hydrocracking a heavy oil, in particular relates to a hydrocracking catalyst composition which comprises metals of Group VIb and Group VIII of the Periodic Table deposited on a carrier material consisting of Y-zeolite and one or more members of the group consisting of alumina-zinc oxide, alumina-boria and alumina-silica-magnesia, said composition having a specific pore diameter and pore size distribution referred to afterwards, and a method of making same.
As a catalyst for use in hydrocracking a heavy oil there is hitherto known one comprising a hydrogenatively active metal deposited on an amorphous inorganic oxide. However, since the catalyst of this type is not so high in activity, there is necessity of adopting such severe reaction conditions as a high reaction temperature or a low liquid hourly space velocity when carrying out a hydrocracking process using said catalyst. In this regard, it is to be noted that adoption of a high reaction temperature promotes deposition of carbonaceous materials or heavy metals such as nickel, vanadium and the like on the catalyst, thereby producing an undesirable result of shortening the catalyst life. On the other hand, when intending to compensate for the low activity of the catalyst by selecting a liquid hourly space velocity, there must be adopted an extremely low liquid hourly space velocity. Hence, it is impossible to find a practical value in the practice of hydrocracking process under such conditions.
For the purpose of improving the low activity of the catalyst of this type, of late there has been developed a zeolite-containing hydrocracking catalyst. This zeolite-containing catalyst displays a high cracking activity as compared with a zeolite-free one, and possesses an ability to hydrocrack a heavy oil at a relatively low temperature. However, the fact is that the zeolite-containing catalyst of this type exclusively relies on the zeolite having a markedly strong solid acidic property for its cracking activity. Therefore, when hydrocracking a heavy oil using this catalyst, it is impossible to selectively produce a middle fraction without sacrificing the conversion to a certain degree. In other words, if the reaction temperature is raised to increase the conversion, it will result in that as the heavy oil feed is cracked into short-chain hydrocarbons more than necessary, the amount of gaseous component to be produced increases that much, whereby the yield of the middle fraction decreases.
The above mentioned problem inherent in the zeolite-containing catalyst, indeed, may be solved in the manner of allotting a part of the cracking activity in said catalyst to a comparatively mild solid acidic substance other than zeolite, for instance, such as boria, magnesia or the like. However, the conventional zeolite-containing catalysts, irrespective of whether they contain relatively mild solid acidic substances or not, are defective in that their active sites are destroyed by the action of asphaltene and the like contained inevitably in heavy oil, due to the lack of sufficient considerationn as to the pore diameter and pore size distribution of catalysts, and consequently their catalytic activity is liable to decay in a relatively short period of time.